an endophytic member of the Erysiphaceae . 
189 
great numbers through the stomata, and form an external mycelium 
(varying in consistence from arachnoid to felted tomentose) on the surface 
of the leaf or stem preparatory to the formation of perithecia. In some 
cases it appears that some of the hyphae which form this external mycelium 
may arise as lateral branches from the conidiophores L The hyphae of the 
external mycelium, in many cases if not in all, nourish themselves by 
sending down branches through the stomata, exactly as in the case of the 
hemi-endophytic mycelium of Phyllactinia (see Palla ( 11 ) ; also Monograph 
( 2 ), p. 4, fig. 163). So far as I have been able to observe from the herbarium 
material available, no haustoria are sent by the external hyphae through 
the cuticle into the epidermal cells. Nevertheless the hyphae which creep 
on the surface of the leaf during the latter part of the conidial stage, and 
throughout the perithecial stage, possess peculiarly shaped short lateral 
branches, which in some cases are very similar to the appressoria on the 
hyphae of ectoparasitic species. These short lateral branches, which are 
figured in Plate XIII, Figs. 4, 20, 21, are often closely applied to the surface 
of the epidermis, and appear to serve the purpose of attaching the hyphae 
to the leaf ; in the herbarium material available I have not been able to 
observe that haustoria are ever produced from these appressoria. It may 
be noted here, as a fact of considerable interest, that the mycelial hyphae 
of the hemi-endophytic species Phyllactinia corylea possess appressoria of 
exactly similar shape, and in this species also no haustoria are sent into the 
epidermal cells from these organs. 
I have been able to observe the early stages of germination of the 
conidium. Living examples of the fungus, in the conidial stage only, 
occurring on Ballota rupestris 1 2 , were kindly sent to me from Sicily by 
Prof. G. Scalia. As, unfortunately, plants of B. rupestris were not available 
for inoculation experiments, I used the leaves of Eryngium campestre i one 
of the host-plants of E. taurica. The leaves which were inoculated were 
treated as follows : At the place of inoculation the upper epidermis and most 
of the underlying mesophyll tissue were cut away, leaving the under epi- 
dermis intact. Conidia were sown on the cuticular surface of the uninjured 
epidermal cells over the wound, and the leaf placed, with the cut surface 
downwards, on damp blotting-paper at the bottom of a closed Petri dish. 
The stages of germination reached by the conidia are shown in Fig. 10. 
It is an interesting fact that the conidium on germination at once forms an 
appressorium, just as is the case with the germinating conidia of the ecto- 
1 This accords with the observations made by Maire (6) in his paper referred to later. This 
author remarks, writing of the superficial mycelium : ‘ II est form£ de tubes beaucoup plus fins que 
le mycelium interne. Ces tubes prennent naissance par ramification laterale des conidiophores pres 
de leur base, ou plus haut, ou encore aux d^pens de filaments speciaux, sortant des stomates en 
meme temps que les conidiophores.’ 
2 This is the form which has been described as Oidium gigasporum (see below, p. 190). 
